The invention relates to an injection molding unit for an injection molding machine for the processing of plastic materials and other plasticisable substances . An injection molding unit of this type is for injecting these substances into a mold which can be fixed on the injection molding machine, ceramic substances or other powdery substances being also considered, for example, as the plasticisable substances to be injected.
An injection molding unit of this type, known in EP 0 662 382 B1, has two electric drives for the screw drive. One motor is for carrying out the rotary motion of the screw, that is for dosing the substance, the other motor is for carrying out the axial displacement of the screw. The two electric drives are configured as hollow-shaft motors and are disposed with their axes in alignment with the axis of the screw and consequently with the axis of injection. To guarantee the interaction of the two motors, they are disposed so as to be displaceable relative to each other, the members driven by the respective rotor engaging one another in a costly manner. Because the two hollow shaft motors nest in one another, they can only be replaced as one unit, which increases both manufacturing costs and servicing costs.
EP 0 723 848 A1 makes known an injection molding unit where two electric drives, configured as hollow-shaft motors, are also used for rotating the screw and for displacing the screw in an axial manner. The motors are disposed in alignment with the axis of injection. To enable displacement of the motors relative to each other, a plurality of spline shafts, which mesh with each other, are provided so that it is possible at any time for either of the motors to displace the feed screw. These spline shafts necessitate tate additional expenditure. The hollow-shaft motors cannot be exchanged independently of one another, at least as far as the rotors of these motors are concerned.
Proceeding from this related the present invention provides a compact injection molding unit which is simple in design in view of expenditure for assembly and maintenance.
The injection molding unit of the present invention includes: a carrier block for the accommodation of a plasticizing cylinder; a feed screw which is disposed in the plasticizing cylinder along an axis of injection for the injection of the plasticisable substances into a mold; an injection bridge, which is displaceable axially along the axis of injection and on which the feed screw is mounted so as to be displaceable via at least one bearing element; an electromechanical injection unit for the axial displacement of injection bridge and feed screw through the intermediary of a linear displacement means driven by a first electric drive, the axis of the first electric drive being aligned with the axis of injection; and an electromechanical dosing unit for rotating the feed screw through the intermediary of a second electric drive, the axis of the second electric drive being aligned with the axis of injection. The first and second electric drives are disposed on the injection bridge on both sides of a parting plane which extends substantially crosswise to the axis of injection and separates the area of influence of the first electric drive from the area of influence of the second electric drive.
The two electric drives are disposed independently of one another on both sides of a parting plane so that there is no need for costly connection mechanisms. Consequently, components of the individual motors must not go beyond their side. Between the electric drives, which are effective in both directions of the parting plane, a passive space can, consequently, be formed which makes it possible for the two motors to be supported on a common supporting member.